You are on the right track! Let's break down the voltage drop calculation and verify your result. Here's the process and the values I get, along with some considerations

Understanding Voltage Drop

Voltage drop is the reduction in voltage as electrical current flows through a conductor. Excessive voltage drop can cause equipment to malfunction, motors to overheat, and lights to dim. The common recommendation is to keep voltage drop under 3% for branch circuits and 5% for feeders.

Formula for Voltage Drop (AC - Three Phase)

The formula we will use is:VD = (1.732 I R L) / 1000Where: VD = Voltage Drop (in volts) 1.732 = Square root of 3 (for three-phase systems) I = Current (Amps) R = Conductor Resistance (Ohms per 1000 feet) L = One-way Length of Conductor (feet) 1000 = Conversion factor to account for resistance typically given per 1000ftValues I (Current)

146 Amps

V (Voltage)

480 Volts

R (Resistance)

You need the resistance of 1/0 AWG copper or aluminum conductor at 75°C. This is critical. Let's use the NEC values for Copper. Chapter 9, Table 8 in the NEC gives the following value.

Copper

0.126 Ohms per 1000 feet

L (Length)

This is what we're solving for to determine the maximum length.

Target Voltage Drop 3% of 480V = 0.03 480V = 14.4 VoltsCalculations (Copper)

Let's rearrange the formula to solve for L (Length):L = (VD 1000) / (1.732 I R)Now, plug in the values for Copper:L = (14.4 1000) / (1.732 146 0.126) = 454.4 ftConclusion

Based on using 1/0 AWG copper wire with a load of 146 amps at 480 volts (3-phase), your approximate maximum run length to stay within a 3% voltage drop is about 454ft.

Important Considerations and Why Your Number Might Differ Slightly


Temperature Correction

The NEC resistance values are at a specific temperature (usually based on the conductor's insulation rating). If the conductor is operating at a significantly different temperature, the resistance will change. In practice this will depend on ambient temperature, number of conductors, and derating factors.2.

Conductor Material

The conductor material is critical. Copper and Aluminum have significantly different resistance values. I have assumed copper in my calculations.3.

Raceway Type

The type of raceway (conduit, cable tray, etc.) affects heat dissipation and thus the conductor temperature.4.

Derating Factors

If multiple conductors are bundled together in a raceway, you may need to apply derating factors, which will effectively increase the resistance.5.

NEC Table 8 vs. Actual Conductor Data

NEC Table 8 provides general resistance values. The manufacturer of the specific wire you're using may provide more precise data.6.

Accuracy of Current

Is 146 amps the absolute maximum continuous load? If it's close, consider upsizing.

Recommendations Verify Conductor Resistance

The most important thing is to get the actual resistance per 1000 ft for the specific wire you plan to use, at the operating temperature, from the manufacturer's data.



Err on the Side of Caution

It's always better to slightly oversize the conductor to minimize voltage drop, especially for critical loads.

Consider Aluminum

Aluminum is a cheaper option.

Double-Check: Always have a qualified electrician review your calculations and the installation. Flag for review